Television system



Nov. 9 1926.

H. c. EGERTON TELEVISION SYSTEM Filed August 24, 1920 2 Sheets-Sheet 1 /n venfor: Henry 6. fyerfan;

Nov. -9 1926. 1,605,930

H. c. EGERTON EEEEE ISI SSSSSS EM Filed August 24, 1920 2 Sheets-Sheet 2 ON. WW MW 0 0 0"0 M //7 van for: HEN/1V C. fyerfon.

b W4 WWU Patented Nov. 9; 1926.

UNITED sTATEs" HENRY c. EGEBTON, or marnnwoon, NEW J RsEY, assmnon 'ro wEsrEmr EnEc'rmc I 1,605,930 PATENT OFFICE.

I COMPANY ,fINCOBPOBATED, OF NEW YORK, N. Y., A CORPORATION OF'NEW YORK.

TELEVISION sYsrEn.

I Application filed August 24, 1920. Serial no. 405,627.

This invention relates to television systems and more particularly to systems for the transmission and production of pictures and -1mages. 5 The transmission of pictures and their re- 7 production at a distant station. has been previously suggested ,and a variety of methods for accomplishing this have been proposed. In general, the methods employed comprise l scanning successively at the transmitting station elementary portions of a picture or image under consideration an the production and transmission of electrical impulses proportional to the intensity of the light emitted by these successive portions. The scanning. operation is accomplished by an element moving with respect to the image and usually consisting of a mirror or light reflecting device adapted to reflect light from the various elementary portions of the image in sequence upon a light sensitive apparatus adapted to produce electrical impulses corresponding to the intensity of the reflected light. After transmission to the receiving station, these impulses serve to correspondingly vary the intensity of a beam of light which is reflected upon a suitable receiving screen or plate. In order that the picture at the receiving station may be a faithful reproduction of that at the transmitting station, it is necessary that the reflected light beam atthe receiving station should traverse a path which corresponds at each instant with the scanning path at the transmitting station. In general, this is accomplished by synchronizing apparatus simultaneously controlling the positions of the analyzing mirror at the transmitting station and of the corres onding light reflecting or image forming mirror at the receiving station.

In employing this method for the trans- -mission of pictures of moving objects, it is necessary that the object at the transmitting end be scanned a sufficient number of times per second to provide for the apparently continuous reproduction of the picture on the receiving screen so. that the observers.

eye can detect no time lag or flicker. This would demand for moving objects that the object should be's'cannedand reproduced at least eighteen to twentytimes per second.

A feature ofthis invention consists in the provision of a single analyzing or scanning element, thus avoiding the'distortions inherent in systems employing two elements.

a definite frequenc Another feature of the invention consists in analyzingthe image at the transmitting station and reforming it at the receiving sta- A further feature of the invention consists in transmission of the impulses representing light intensities and the synchronizingcurrents for the'analyzing and image forming mirrors as waves of different frequencies which may accordingly be transmitted over the same circuit in the case of wire transmission, or as impulses of the same carrier wavein the case of radio transmission.

According to the present invention, an analyzing mirror at the transmitting station and apicture-forming mirror at the receiving station are each mounted for oscillation about two axes at right angles to each other. A current of one frequency operatin a magnetic unit at each station gives eac mirror continuous oscillation about one axis. urrent of another frequency operating diflerent magnetic units maintains each mirror in continuous oscillation about its other axis at another frequency. Impulses corresponding to the light intensities of the successive elementary areas may be made to occur at a frequency widely different from that of the synchronizing currents. The two synchronizing currents and the light intensity or image current may therefore be readily transmittedover a common circuit and separated at the receiving station. The synchronizing currents at the receiving station control the movement, of a picture-forming mirror which is caused to reflect a beam of light along the path correspond ng to that of the analyzer at the transmitting station. In order to secure a' varia tion in light at the receiving station corresponding to the intensity of the transmitted impulses or image current, a screen of varying translucency is placed between a source of light and a mirror which is movable in response to the received image currents. These currents therefore vary the position of the mirror with respect to the screen and cause it to select beams of different intensity for reflection'upo'n the picture forming mirror. Thereflected beam of light varying in intensity in accordance with the reflected beam at the transmitting station and illumifier systems nating a path corresponding to the scanning path at the transmitting station reproduces the image which it is desired to transmit.

In the drawing, Fig. 1 illustrates diagrammatically the circuit arrangements 0 a system embodying the "invention; Fig. 2 illustrates the scanning element and Fig. 3, the path through the successive elements of an image as scanned by an analyzing mirror.

link 8 with the member which it drives.

The motor 7 is preferably of the type disclosed in Patent No. 1,232,514, issued July 10, 1917, to applicant for electrical ampliand consists in an electromagnetic core having two poles provided with windings 9 and 10 connected in such relation that opposite magnetic polarities are given the two poles. The poles are also provided with line or operating windings 11 and 12, which act to increase the magnetic pull at one end of the armature, while decreasing that at the other, all in well-known manner. Suitable bearings at the middle pole piece of the motor 7 permit the armature to move reciprocally in a rocking manner in unison with reversals or changes in amplitude of the currents through line windings 11 and 12, thereby causing the driven members to undergo oscillations at a corresponding rate. The picture forming mirror and its operating motors at the receiving station are in every respect similar to the corresponding analyzing apparatus at the transmitting station.

Sources 0 and 0 of alternating current which may be of any type but are preferably of the highly evacuated three-element electron discharge type, produce currents of different frequencies, as for example, of 123 cycles and 101 cycles, respectively;

At the transmitting and receiving stations, filters F and F are bridged across lines 13 but any suitable connection of the filters to the line may be employed. Filters F are of the band-pass type and may be designed to transmit oscillations of a band of frequencies from 105 cycles to 125 cycles and to exclude currents of frequencies out side these upper and lower cut-off frequencies of the band. Filters F may be of the low-pass type and so designed as to trans- Referring to Fig. 1, an image 1 to be mit only currents of frequencies lyingbef plies it to one of the electromagnetic motors 7 through an amplifier A, preferably of the well-known thermionic type. 'At the receiving station phase changing devices 24 eachcomprising variable bridging resistance a variable coupling series transformer and a switch for reversing connections and provided to secure proper phase adjustment of the synchronizing or motor operating currents. As is well-known, currents of different frequencies are differently retarded by an ordinary transmission line. The phase adjusting device permits the motions of the electromagnetic motors to be given the proper relative phase with respect to each other and with respect to the image currents. The various loading and phase equalizing devices employed in te lephony and other signaling may be used in addition to the phase adjusting devices illustrated tocorrect the phases of both the synchronizing and image currents.

It will be clear that with the apparatus as described, the sources 0 and O will supply two different frequency currents to line 13, and that the analyzing and picture forming mirrors will each oscillate at a constant amplitude on one axis at the frequency of one of these currents and at a constant amplitude about another axis at the frequency of the other current. At the transmitting station a light sensitive or photo-electric device represented by 14 is so positioned as to receive the beam of light from image 1 as reflected by the scanning device 2. This photo-electric element may be of the selenium or of the acuum type employing a photo-sensitive metal, such as potassium or sodium.

The photo-electric device l t operates in conjunction with a source of current 15 in well-known manner. The light from various points of the picture is reflected in sequence into the photo-electric element and the changes from dark to light enable the transmission of an alternating current higher in frequency than either of the two synchronizing frequencies, the frequency and wave form of this alternating image current varying with the size, definition, and depth of the shadows. That this frequency is higher than either of the synchronizing frequencies' will be obvious when it is remembered that there are two lines across the picture for each cycle of the synchronizing current, and if a shadow occurs once in the picture, it must be crossed twice for each cycle of the synchronizing current. It is also to be remembered that although there I 'be the same as if, several transmitted, because the interval between are sufliciently sharp in definition, the effect on the frequencies of the ima' e current'may undred were zero and maximum of the image currents will be determined by the sharpness of the shadow and will have no definite relation to the length of the shadow.

The repeater 16 serves to impress upon the line' 13 corresponding amplified image currents, the frequency of which is considerably higher than that of the motor operating or synchronizing currents. At the receiver these image currents are selected by filter 17 and after amplification by thermionic repeaters are passed through the mirror conducting supports 18 of an oscillograph type instrument comprising means such as a permanent magnet 19 for subjecting the supports 18 to the action of a magnetic field. The mirror 20 actordingly oscillates with its supports 18. A source of light 21 is placed behind a-screen 22 of translucency varying from one side to the other so that the light transmitted therethrough and from its sur-' face varies in intensity from one side to the other. As mirror 20 is caused to oscillate, it successively. reflects beams of different intensities on the picture-forming mirror at the receiving station. Since the pictureforming mirror is tracin a path of light on the screen 28 correspon ing to that of the scanning path at the transmitter, and the intensity of the reflected light at the re-- ceiver is varied in accordance with the variations of image current supplied to line 13 by the photo-electric source 14, the image 1 will be reproduced on screen 23.

Fig. 3 shows the path of the successive areas of the image from which the analyzing source reflects light. In this figure the path is that which would be obtained by giving the two synchronizing currents frequencies of 13 and 18, respectively. The heavy lines indicate the course of a few cycles of the path to show how the analyzer and the picture-former analyze and reform the picture uniformly.

The ordinary single line scanning device traces a path moving back and forth near one margin of the image and slowly rogressing toward the opposite margin. he path of the heavy line of Fig. 3 moves fairly uniformly over the entire image area during the first few cycles. It results, therefore, that each portion of the image receives some illumination and the picture evolves first dimly as the operation begins and then clearly when the entire area has been once traversed. In order to secure a scanning motion of the mirror which will cause it to traverse as nearly as possible the entire surface of the image, the oscillation frequencies of the two electromagnetic motors should preferably be made incommensuraper second is determined by thegreatest common denominator of the two synchronizing frequencies.

In operation according to the diagram of Fig. 3 in which the synchronizing frequencies have been chosen for simplicity, as 13 and 18, respectively, the image will be repeated once a second. With the frequencies of 101 and 123 cycles, the image will be repeated once each second. Since each oscillation gives two lines crossing the image, there will be 246 lines in one direction and 202 in the other. If the picture is, for example, 3x 4:" in area, this will mean approximately 60 lines per inch.

The dimensions of the area at the transmitting station and of the image formed at the receiving station depend upon the amplitudes of the synchronizing oscillations and the consequent amplitudes of the mirror oscillations. It is therefore possible to in-' crease or decrease the size of the reproduced picture at will by merely correspondingly changing the amplifying power of the amplifiers. A conventional potentiometer input circuit to permit this is illustrated. If at any time during operation of the sys tem, the transmitting operator desires to transmit a larger or a smaller picture, he. need merely signal to the receiving station the change in dimensions and the receiving operator may then change the amplification of the amplifiers. This involves no change or adjustment of the frequencies of the oscillators and filter constants. It is of course to be understood that the precise synchronizing frequencies may be varied within wide limits and that those given in the preceding description are merely by way of illustration.

The screen on. which the image is formed at the receiving station may consist of a plate of ground glass, but ifdesirable any other suitable type of screen may be employed. In order to retain theimage on the ground glass plate for a short time to accentuate the effect of retention on the ret ina of the eye, the ground glass may be coated with luminous paint similar to the well-known phosphorescent paints, or any other suitable means for making the screen phosphorescent may be employed; After the light has been flashed across it several times, the residual glow will indicate the image. I

At the transmitting station, if the picture onto the is to be transmitted, a concave scanning mirror may be used instead of a flat mirror, and by this means a beam of light reflected hoto-electric element is concentrated. I on the other hand, the image of an object is to be transmitted, a flat mirror of small dimension may be used or the image ma be focused on a ground glass screen an then scanned by a concave mirror. In order to increase the definition of the scanning operation, the aperture or opening in front of the photo-electric element through which the reflected light from the image must pass is preferably made very small. At the receiving station the image may be focused on the screen in well-known manner by the use of a series of lenses and concave mirrors having proper focal lengths,

These same principles may be applied to radio and to carrier current operation in Which the two synchronizing currents and the image may each be transmitted as modulations of the same or of different frequency carrier waves.

WVhat is claimed is:

1. A mirror, means for causing said mir- .ror to simultaneously execute continuous oscillations of constant amplitude in two directions, and means for fixing the amplitude of said oscillations at any desired val ues.

2. A mirror, means for causing said mirror to simultaneously execute continuous oscillations of constant amplitude in two directions at different rates, and adjusting means for fixing the amplitude of said osci'llations at any desired values.

3. In combination. an analyzing device,

I an image forming device, a line connecting said devices, means for supplying to said line, currents of two different frequencies to cause said devices to execute similar move ments, means for transmitting over said line from said analyzing device to said image device, energy varying in accordance with that of light incident upon said analyz- 'ing device, and adjusting means associated with said image forming device for controlling the size of the image formed thereby.

4. A system for the transmission of images comprising a scanning element, an image forming element, a line connecting said elements, means for supplying currents of one frequency to the line to cause each of said elements to execute oscillations of the same frequency, means to simultaneously supply current of another frequency to the line to cause each element to execute other frequency oscillations, and adjusting means associated with said image forming element for controlling the amplitude of the currents received over said line for correspondingly controlling the size of the image formed.

5. In combination, an analyzing device, an

image forming device, a line connecting said devices, means for supplying to said line, currents of two different frequencies to cause said devices to execute similar movements, means for transmitting over said line from said analyzing device to said image device energy varying in accordance with that of light incident upon said analyzing device, and means for adjustingthe phase relation between said currents of different frequencies supplied to said image forming device independently of the phase relation between said currents of different frequencies supplied to said line.

6. In an image transmission system, a plurality of sources of synchronizing currents of different frequencies, and a source of current of a frequency different from that of said synchronizing currents for controlling the intensity of the light reproducing the image, a common line for transmitting said currents, means at the terminal of the line at which the image is to be reproduced for selecting from said line said currents of different frequencies and means controlled by said selected currents to reproduce the image being transmitted, said last mentioned means comprising current adjusting means for controlling the size of the image produced.

' 7. In combination an analyzing device, an image forming device, a transmission circuit extending between said devices, means for supplying to said transmission circuit currents of two different frequencies to cause said devices to execute similar movements in synchronism, means for transmitting over said circuit from said analyzing device to said image device energy varying in accordance with the elemental tone values of the image to be transmitted, and adjusting means associated with said image forming device for controlling the amplitude of the energy variations imparted thereto.

8. The method of picture transmission, which comprises scanning the picture area in groups of scannings, each group consisting of more than two scannings in succession, the different scannings of a group traversing different paths, and corresponding scannings of different groups starting at the same point of the picture area.

9. In a system for transmitt ng pictures, scanning means comprising a mirror adapted to be moved about coordinate axes, and two sources of alternating current of sinusoidal wave forms and different frequencies, one of said currents effective to move said mirror about one of said axes, the other ofsaid currents effective. to simultaneously az -ive' said multaneously execute continuous oscillations of a constant amplitude in two directions,

amplifying devices having input and output circuits for amplifying the currents from said sources, and means in the input circuits of said amplifying devices for controlling the amplitude of oscillation of said mirror.

11. In combination, a mirror, two separate sources of alternating current for causing said mirror to simultaneously execute continuous oscillations of a constant amplitude in two separate directions, thermionic amplifying devices having input and output circuits for amplifying currents from said sources, and means for adjusting the input circuits of said amplifying devices to regulate the amplitude of oscillation of said mirror to any desired value.

' 12. A system for the transmission of images comprising a scanning element, an image forming element, a line connecting said elements, two sources of alternating current each of a different frequency connected to said line, band filters each designed to selectively pass current of one frequency and to exclude the other, means responsive to said currents after passing said filters for causing said elements to execute in separate directions oscillations of the same frequencies as said currents, and means for applying to said line a current varying in accordance with the li hts and shades of the image to be transmitte In witness whereof, I have hereunto subscribed my name this ninth day of August A. D., 1920.

HENRY C. EGERTON. 

